The organic electroluminescent element (hereunder “EL” will also be used as the abbreviation of the term “electroluminescence” or “electroluminescent”) is a spontaneously light-emitting or self-light-emitting element which makes use of such a principle that a fluorescent substance undergoes light-emission by the energy generated through the recombination of holes injected through the anode with electrons injected through the cathode, when an electric field is applied to the organic EL element. Organic EL elements composed of organic materials have vigorously been studied by a variety of research institutions, since C. W. Tang et al. of Eastman Kodak Co. reported a low voltage-operable organic EL element composed of a laminated element (see, for instance, C. W. Tang, S. A. Vanslyke, Applied Physics Letters, 1987, 51:913). Tang et al. employ tris-(8-quinolinolato) aluminum in a light-emitting layer and a triphenyl-diamine derivative in a hole-transporting layer. The use of a laminated structure will be advantageous in, for instance, that it can increase the efficiency of injecting holes into the light-emitting layer, that it can block the electrons injected through the cathode to thus improve the generation efficiency of excitons formed through the recombination holes with electrons and that it permits the restraint of the generated excitons in the light-emitting layer. Examples of the structures of such organic EL elements well known in the art like the example discussed above include a two-layer structure comprising a hole-transporting (or hole-injecting) layer and an electron-transporting and light-emitting layer; and a three-layer structure comprising a hole-transporting (or hole-injecting) layer, a light-emitting layer and an electron-transporting (or electron-injecting) layer. In respect of the element having such a laminated structure, there have variously been investigated and devised, the structures of such an element and the production methods thereof.
In addition, light-emitting materials known in this art include, for instance, chelate complexes such as tris-(8-quinolinolato) aluminum complex; and light-emitting materials such as coumarin derivatives, tetraphenyl butadiene derivatives, bis-styryl-arylene derivatives, and oxadiazole derivatives. In this respect, it has been reported that these substances permit the emission of light rays whose wavelengths fall within the visible light region extending from blue to red light rays and there has accordingly been desired for the development of a color-display element using, for instance, these substances (see, for instance, Patent Document 1, Patent Document 2 and Patent Document 3 specified below).
Moreover, Patent Document 4 and Patent Document 5 disclose elements which make use of bis-anthracene derivatives as light-emitting substances. In this connection, the bis-anthracene derivatives are used as materials capable of emitting blue light rays, but they have still been insufficient since they can never provide the efficiency and lifetime of practically acceptable levels.
Furthermore, there have been disclosed elements which make use of symmetrical pyrene derivatives as light-emitting substances in Patent Document 6, Patent Document 7, Patent Document 8 and Patent Document 9. Such symmetrical pyrene derivatives can be used as materials capable of emitting blue light rays, but it has been found that these elements are insufficient in their lifetime and accordingly, there has been desired for the further improvement of the lifetime thereof.
Further, Patent Document 10, Patent Document 11 and Patent Document 12 disclose elements which make use of fluoranthene compounds as light-emitting substances. Such fluoranthene compounds can be used as materials capable of emitting blue light rays, but the resulting elements have likewise been required for the further improvement of the lifetime thereof.
Patent Document 1: Japanese Un-Examined Patent Publication Hei 8-239655;
Patent Document 2: Japanese Un-Examined Patent Publication Hei 7-138561;
Patent Document 3: Japanese Un-Examined Patent Publication Hei 3-200889;
Patent Document 4: Japanese Patent No. 3,008,897;
Patent Document 5: Japanese Un-Examined Patent Publication Hei 8-12600;
Patent Document 6: Japanese Un-Examined Patent Publication 2001-118682;
Patent Document 7: Japanese Un-Examined Patent Publication 2002-63988;
Patent Document 8: Japanese Un-Examined Patent Publication 2004-75567;
Patent Document 9: Japanese Un-Examined Patent Publication 2004-83481;
Patent Document 10: Japanese Un-Examined Patent Publication 2002-69044;
Patent Document 11: International Publication No. 02/085822 pamphlet;
Patent Document 12: International Patent Publication No. 2005/033051 pamphlet